U.S. patent application number 13/024190 was filed with the patent office on 2012-02-09 for device for determining the position of at least one structure on an object, use of an illumination apparatus with the device and use of protective gas with the device.
This patent application is currently assigned to VISTEC SEMICONDUCTOR SYSTEMS GMBH. Invention is credited to Michael Heiden.
Application Number | 20120033230 13/024190 |
Document ID | / |
Family ID | 39628250 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120033230 |
Kind Code |
A1 |
Heiden; Michael |
February 9, 2012 |
Device for Determining the Position of at Least One Structure on an
Object, Use of an Illumination Apparatus with the Device and Use of
Protective Gas with the Device
Abstract
A device for determining the position of a structure (3) on an
object (2) in relation to a coordinate system is disclosed. The
object (2) is placed on a measuring table (20) which is movable in
one plane (25a), wherein a block (25) defines the plane (25a). At
least one optical arrangement (40, 50) is provided for transmitted
light illumination and/or reflected light illumination. The optical
arrangement (40, 50) comprises an illumination apparatus (41, 51)
for reflected light illumination and/or transmitted light
illumination and at least one first or second optical element (9a,
9b), wherein at least part of the at least one optical element (9a,
9b) extends into the space (110) between the block (25) and an
optical system support (100). The block (25) and/or the optical
system support (100) separates the illumination apparatus (41, 51)
spatially from the plane (25a) in which the measuring table (20) is
movable.
Inventors: |
Heiden; Michael;
(Wolfersheim, DE) |
Assignee: |
VISTEC SEMICONDUCTOR SYSTEMS
GMBH
Weilburg
DE
|
Family ID: |
39628250 |
Appl. No.: |
13/024190 |
Filed: |
February 9, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12015437 |
Jan 16, 2008 |
7903259 |
|
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13024190 |
|
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|
60889595 |
Feb 13, 2007 |
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Current U.S.
Class: |
356/614 |
Current CPC
Class: |
G01B 11/002 20130101;
G03F 1/84 20130101; G03F 7/70625 20130101; G01B 9/02012 20130101;
G01B 9/02027 20130101; G01B 9/02082 20130101 |
Class at
Publication: |
356/614 |
International
Class: |
G01B 11/14 20060101
G01B011/14 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2007 |
DE |
102007007660.8 |
Oct 11, 2007 |
DE |
102007049133.8 |
Claims
1. The use of protective gas in a device for determining the
position of at least one structure on an object, wherein at least
one optical component in a path of the light from at least one
illumination apparatus to at least one optical element is
surrounded by protective gas.
2. The use according to claim 1, wherein all the optical components
in the path of the light from the at least one illumination
apparatus to the optical elements are surrounded by protective gas,
wherein, for this purpose, the optical components are surrounded by
an encapsulation and the light from the at least one illumination
apparatus runs within the encapsulation.
3. The use according to claim 1, characterized in that the optical
components comprise at least one shutter, at least one beam
attenuator, at least one apparatus for speckle reduction and/or at
least one homogeniser, as well as at least one optical element.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 12/015,437, filed on Jan. 16, 2008, which, in turn, claims
priority to German Patent Application No. 10 2007 007 660.8 filed
on Feb. 13, 2007, and German Patent Application No. 10 2007 049
133.8, filed on Oct. 11, 2007, and which also claims the benefit
under 35 U.S.C. 119(e) of U.S. Provisional Application No.
60/889,595, filed on Feb. 13, 2007, all of which are incorporated
herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a device for determining
the position of a structure on an object. In particular, the
invention relates to a device for determining the position of a
structure on an object in relation to a coordinate system. The
object is placed on a measuring table which is movable in one
plane, wherein a block defines a plane in which the measuring table
is movable. At least one laser interferometer for determining a
positional displacement of the measuring table in the plane is
further provided. At least one optical arrangement is provided for
transmitted light illumination and/or reflected light
illumination.
[0003] The invention further relates to the use of at least one
illumination apparatus with a device for determining the position
of at least one structure on an object.
[0004] The invention further relates to the use of protective gas
with a device for determining the position of at least one
structure on an object.
[0005] A measuring device for measuring structures on masks or
substrates used for the production of semiconductors is known from
the lecture manuscript "Pattern Placement Metrology for Mask
Making" by Dr. Carola Blasing. The lecture was given on the
occasion of the Semicon Education Program congress in Geneva on 31
Mar. 1998. This lecture manuscript discloses the basis of a device
for determining the positions of structures on a substrate. With
regard to the details of the operation and the structure of a
device of this type, reference should be made to FIG. 1 of this
patent application, which illustrates the prior art.
[0006] In measuring equipment and devices of the prior art, optical
sensing methods are still favored, although the measuring accuracy
required (currently in the region of a few nanometers) lies far
beneath the resolution achievable with the light wavelength used
(the spectral region of the near UV). The advantage over devices
that operate using optical measuring methods lies essentially in a
less complex design and easier operation compared with systems
using other sensing systems, for example, with X-rays or electron
beams.
[0007] A measuring device for measuring structures on a transparent
substrate is also disclosed by the published application DE 198 19
492. The measuring device comprises a reflected light illumination
apparatus, an imaging device and a detector device for imaging the
structures on the substrate. The substrate is placed on a
displaceable measuring table which can be displaced perpendicularly
to the optical axis. The position of the measuring table is
determined by interferometric means. The detector apparatus
registers the edge profiles created by the structures. Based on the
profiles, the position of the edges of the respective structure can
be deter-mined in relation to a fixed coordinate system.
[0008] A device of this type is disclosed, for example, in DE 199
49 005, DE 198 58 428, DE 101 06 699 and DE 10 2004 023 739. In all
these prior art documents, a coordinate measuring machine is
described with which structures on a substrate can be measured. The
substrate is placed on a measuring table which can be moved in the
X-coordinate direction and in the Y-coordinate direction. Suitable
light sources are used for illuminating the substrate. The
substrate can be illuminated either by transmitted light and/or by
reflected light. For imaging the illuminated structures, a
measuring objective which is also arranged in the reflected light
ray path is provided. The light collected by the objective lens is
directed to a detector which, in conjunction with a computer,
converts the received signals into digital values.
[0009] The structures on wafers or the masks used for exposure
permit only extremely small tolerances. In order to check these
structures, a very high degree of measuring accuracy (currently in
the nanometer range) is needed. A method and a measuring device for
determining the positions of these structures are disclosed in the
German specification laid open to inspection DE 100 47 211 A1. For
details of the positional determination described, reference is
therefore expressly made to this document.
[0010] Previously, devices for measuring masks or structures on
masks have used mercury-xenon lamps for illuminating the measuring
optical system. These have a very marked intensity maximum in their
spectrum at 365 nm. This wavelength or the region round this
wavelength is used for illuminating the measuring optical system.
The energy in this line has previously been sufficient for
illuminating the measuring optical system. In future systems, due
to the increased demands placed on the resolving power, it will be
necessary to change over to ever shorter wavelengths (248 nm, 193
nm, 157 nm). This higher resolution will be demanded by customers
since the structures on the masks are becoming ever smaller.
However, at these wavelengths, the lamps typically used for
illumination in microscopes do not produce any spectral lines of
sufficient intensity. It is therefore necessary to make use of
alternative light sources or alternative configurations of the
device for measuring structures on a substrate. The necessary
spectral lines are not present at sufficient intensity in the
wavelength range required here.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of the present invention to
provide a device with which it is possible to carry out examination
of masks and substrates with smaller structures. In addition, the
range within which the object to be measured is moved must not be
influenced by heat production from possibly suitable illumination
apparatus.
[0012] This object is solved with a device for determining the
position of a structure on an object in relation to a coordinate
system, the device comprises a measuring table carrying the object,
wherein the measuring table is movable in a plane, a block defines
the plane, wherein at least one laser interferometer system is used
for determining a positional change of the measuring table in the
plane, at least one optical arrangement is provided for transmitted
light illumination and/or reflected light illumination of the
object, an illumination apparatus for reflected light illumination
and/or transmitted light illumination and at least one optical
element are provided, wherein at least one part of the at least one
optical element extends into a space formed between the block and
an optical system support, wherein the block and/or the optical
system support spatially separates the illumination apparatus from
the plane in which the measuring table is movable.
[0013] It is a further object of the invention to design an
illumination apparatus for use with a device for determining the
position of at least one structure on an object such that the
device can be used to measure objects with smaller structure
separations.
[0014] The above object is solved by use of at least one
illumination apparatus in a device for determining the position of
at least one structure on an object, wherein the at least one
illumination apparatus is provided in the reflected light
illumination apparatus and/or the transmitted light illumination
apparatus, and that the illumination apparatus provides light for a
first optical element and/or light for a second optical element and
that at least one system for triggering the illumination light is
assigned to the illumination apparatus.
[0015] It is a further object of the invention to design a device
for measuring structures on objects such that the service life of
the optical components is extended.
[0016] The above object is solved the use of protective gas in a
device for determining the position of at least one structure on an
object, wherein at least one optical component in the path of the
light from at least one illumination apparatus to at least one
optical element is surrounded by protective gas.
[0017] When determining the position of a structure on an object in
relation to a coordinate system, it is advantageous if the object
is placed on a measuring table that is movable in one plane. A
block is provided which defines the plane in which the table can be
moved. Furthermore, at least one laser interferometer for
determining the positional displacement of the measuring table in
the plane is provided. At least one optical arrangement is provided
for transmitted light illumination and/or reflected light
illumination. The optical arrangement also comprises an
illumination apparatus for reflected light illumination and/or
transmitted light illumination of at least one optical element. At
least one part of the at least one optical element is provided in
the space formed between the block and the optical system support.
The block and/or the optical system support separates the
illumination apparatus from the plane in which the measuring table
is movable.
[0018] The illumination apparatus comprises as the light source at
least one excimer laser or at least one frequency multiplied
solid-state laser or gas laser or at least one excimer lamp. The at
least one optical element which represents an objective lens is
designed as a high-resolution microscope objective which forms an
image of the structure on the surface of the object under reflected
light and/or transmitted light in the spectral range of the near UV
on at least one detector.
[0019] There are several advantageous embodiments of the device
with which the invention can be realized. For example, the
illumination apparatus is mounted only in the reflected light
arrangement and the first optical element is mounted opposing the
object in the reflected light arrangement. In this embodiment, the
first optical element is an objective lens. A further possibility
is that the illumination apparatus is only mounted in the
transmitted light arrangement. The second optical element is then
mounted under the object in the transmitted light arrangement. The
second optical element is a condenser. This arrangement can also be
regarded as a reflected light arrangement if the object is placed
in the measuring table such that the structures present on the
surface of the object face in the direction of the second optical
element. In this orientation of the object, the second optical
element is also an objective lens (microscope objective). This
arrangement has the advantage that the objects, masks or substrates
are placed in the same orientation in the device as the masks,
objects or substrates are placed when used in a stepper for the
production of the semiconductors.
[0020] In a further advantageous embodiment of the device, the
illumination apparatus makes light available for reflected light
illumination and for transmitted light illumination. The first
optical element is mounted as an objective lens opposite the object
in the reflected light arrangement and the second optical element
in the form of a condenser is mounted under the object in the
transmitted light arrangement. It is also conceivable for separate
light sources to be provided for reflected light illumination and
transmitted light illumination.
[0021] For the light source of the illumination apparatus, it is
advantageous to use an excimer laser at a wavelength of 157 nm or
248 nm. A frequency-multiplied solid-state laser or gas laser with
a wavelength of 266 nm, 213 nm or 193 nm can also be used as the
light source for the illumination apparatus. An excimer lamp for
the typical excimer laser lines can also be used.
[0022] The optical arrangement used with the device for measuring
structures on a substrate can comprise in the illumination branch
for reflected light illumination and/or transmitted light
illumination, respectively, at least one apparatus for speckle
reduction and/or at least one shutter and/or at least one
homogenizer and/or at least one beam attenuator.
[0023] A possible arrangement of the various components of the
optical arrangement in the first illumination branch is that the
illumination apparatus has a beam attenuator connected downstream
of it. Following the beam attenuator are the shutter, the apparatus
for speckle reduction and the homogenizer. Once the light beam
leaves the homogenizer, it reaches the first optical element.
Furthermore, the illumination apparatus can also have a beam
monitor assigned to it. With the beam monitor, the intensity of the
light emerging from the illumination apparatus or the light source
can be checked. Depending on the result of the checking, adjustment
of the intensity of the illumination apparatus can be carried out
so that, finally, the same intensity al-ways falls on the object to
be measured.
[0024] A deflecting minor which directs the light from the
illumination apparatus in the first illumination branch through the
optical system support to the first optical element is provided.
This is only the case if the light from the illumination apparatus
runs parallel to, and over, the optical system support. If the
illumination apparatus with the beam attenuator, the shutter, the
apparatus for speckle reduction and/or the homogenizer is mounted
under the block, that is, in the second illumination branch, then
again a deflecting mirror which directs the light from the
illumination apparatus through the block to the second optical
element is also provided.
[0025] The illumination apparatus can also be arranged laterally on
the device. Given a lateral arrangement of the illumination
apparatus, the beam attenuator and the beam monitor can also be
assigned to the illumination apparatus. This lateral arrangement is
advantageous because, for cooling the illumination apparatus, an
air stream can be directed unhindered towards the illumination
apparatus and the additional components which generate a
substantial amount of heat. The object is to conduct away the
dissipation heat in order that the heat generated does not
influence the device and finally also the measuring results
obtained with the device.
[0026] In an advantageous embodiment of the invention, one
illumination apparatus is provided. The light emerging from the
illumination apparatus is led or guided by suitable deflecting
means or by dividers which divide the beam emerging from the
illumination apparatus into the first illumination branch, which
runs substantially parallel to the optical system support, and into
the second illumination branch, which is provided under the block.
In order to enable passage of the beam through the block, suitable
perforations are provided in the block. For the event that the
illumination branch runs parallel to, and over, the optical system
support, a suitable recess is provided in the optical system
support, which enables the passage of the illumination light.
[0027] The shutter used with the device can be configured as an
obstructer or as a pivoting minor or as a movable divider or minor.
A beam attenuator can be provided in the first or second
illumination branch. The beam attenuator consists of a filter wheel
on which plates having different transmittance values are arranged.
According to need, the relevant plate can be moved by the filter
wheel into the beam path of the first or second illumination
branch. Furthermore, the plates can have different reflection
values. A further possible embodiment of the variable beam
attenuator is that the angle of incidence of the light from the at
least one illumination source onto an inclined and coated substrate
is varied. The attenuated light from the light source that is
transmitted through the coated substrate can be further used in the
device. The inclined and coated substrate causes a beam offset.
This beam offset can be compensated for by a further inclined
substrate. The angular position of the individual substrates can be
varied with motors.
[0028] The illumination apparatus for the reflected light or
transmitted light illumination has a homogenizer for the field
illumination and/or a homogenizer for the pupil illumination of the
first optical element and/or the second optical element.
[0029] The homogenizer can have different configurations. It can
comprise a plurality of microlenses. It can also be configured as a
hexagonal array of microlenses. An orthogonal array of microlenses
is also conceivable. The microlenses can also be configured as a
cylindrical lens array, wherein two crossed cylindrical lens arrays
are provided. The microlenses can also have an aspherical surface.
A further embodiment of the homogenizer is that a diffractive
element is provided. The homogenizer can also consist of a light
mixing rod.
[0030] An apparatus for speckle reduction can be provided in the
first illumination branch and/or in the second illumination branch.
The speckle reduction apparatus can be diffractive in design. The
apparatus for speckle reduction can also be configured as a
diffusion screen. A further design possibility for the apparatus
for speckle reduction is a mode mixing fiber.
[0031] The illumination apparatus is fastened to the device with a
material of low thermal conductivity in order to reduce the heat
conduction to the optical system support and/or to the block. In
order to be able to transport away the dissipation heat
effectively, cooling ribs are also provided. As already mentioned,
an air stream is directed towards the illumination apparatus in
order to increase the effectiveness of the removal of dissipation
heat.
[0032] Advantageously, a climate chamber is provided, wherein the
at least one illumination apparatus is arranged outside the climate
chamber. By this means, the influence of the dissipation heat
generated by the illumination apparatus on the remaining components
of the device is substantially reduced. The climate chamber can be
filled, for example, with a protective gas. Nitrogen has proved
useful as a possible protective gas. The light from the
illumination apparatus passes via windows into the interior of the
climate chamber.
[0033] A further advantageous embodiment of the invention is the
use of at least one illumination apparatus in a device for
determining the position of at least one structure on an object.
The at least one illumination apparatus may be provided in the
reflected light illumination apparatus and/or the transmitted light
illumination apparatus. The illumination apparatus provides light
for a first optical element and/or light for a second optical
element. The illumination apparatus has at least one shutter
assigned to it. As already mentioned, the illumination apparatus is
provided with a light source which comprises at least one excimer
laser or at least one frequency multiplied solid-state or gas laser
or at least one excimer lamp as the illumination source.
[0034] A further advantage of the invention is the use of
protective gas in a device for determining the position of at least
one structure on an object. At least one optical component in the
path of the light from at least one illumination apparatus to at
least one optical element is surrounded by protective gas.
[0035] It is particularly advantageous if all the optical
components in the path of the light from the at least one
illumination apparatus to the optical elements are surrounded by
protective gas. For this purpose, the optical components are
surrounded by an encapsulation and the light from the at least one
illumination apparatus passes within the encapsulation. The
protective gas in the encapsulation is nitrogen, since it is
particularly readily and economically available.
[0036] Further advantageous embodiments and uses of the invention
are contained in the subclaims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The exemplary embodiments of the invention and their
advantages will now be described in greater detail by reference to
the accompanying drawings, in which:
[0038] FIG. 1 shows in schematic form a device for measuring
structures on a substrate, as has long been known from the prior
art.
[0039] FIG. 2 shows an embodiment of the device, wherein the
optical device is arranged together with the illumination apparatus
over an optical system support.
[0040] FIG. 3 shows a further configuration of the embodiment of
FIG. 2, wherein the illumination apparatus also has a beam monitor
assigned to it.
[0041] FIG. 4 shows an embodiment of the device, wherein the
illumination apparatus is arranged laterally on the device and
wherein an air stream is directed onto the illumination
apparatus.
[0042] FIG. 5 shows an embodiment of the invention, wherein the
second illumination branch is arranged under the block and wherein
the light from the illumination apparatus is directed onto the
second optical element.
[0043] FIG. 6 shows an embodiment of the invention, wherein the
illumination apparatus also has a beam monitor assigned to it.
[0044] FIG. 7 shows an embodiment of the invention similar to the
embodiment of FIG. 6, wherein the illumination apparatus is mounted
laterally on the device.
[0045] FIG. 8 shows an embodiment of the invention, wherein in the
first illumination branch and in the second illumination branch, in
each case, an illumination apparatus is provided.
[0046] FIG. 9a shows a substrate, which is placed on the table such
that the structures face in the direction towards the first optical
element.
[0047] FIG. 9b shows the substrate, which is placed on the table
such that the structures on the substrate face in the direction of
the second optical element.
[0048] FIG. 10 shows an embodiment, wherein the illumination
apparatus is provided over the optical system support, and the
light from the illumination apparatus is fed into the first
illumination branch and into the second illumination branch.
[0049] FIG. 11 shows a further embodiment of the invention, which
differs from the embodiment of FIG. 10 in that the illumination
apparatus is arranged under the block.
[0050] FIG. 12 shows an embodiment similar to the embodiment of
FIG. 11, wherein the illumination apparatus is mounted laterally on
the device.
[0051] FIG. 13 shows a further embodiment, wherein the illumination
apparatus is also mounted laterally on the device, but the light
from the illumination apparatus cannot be conducted through the
optical system support or the block into the first illumination
branch or the second illumination branch.
[0052] FIG. 14 shows an embodiment of the invention which is
similar to the embodiment of FIG. 13, wherein the two outputs of
the illumination apparatus each have a shutter and a beam
attenuator assigned to them.
[0053] FIG. 15 shows an embodiment, wherein the illumination
apparatus is an excimer laser.
[0054] FIG. 16 shows an embodiment of the illumination apparatus
which is also configured as an excimer laser, wherein the excimer
laser has a first and a second output.
[0055] FIG. 17 shows an embodiment of the invention, wherein the
device is arranged largely within a climate chamber.
[0056] FIG. 18 shows an embodiment, wherein all the optical parts
of the first illumination branch or of the second illumination
branch are arranged within an encapsulation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] FIG. 1 shows a schematic representation of a coordinate
measuring machine as has long been known from the prior art. The
coordinate measuring machine is identified in the further
description as a device. It should also be noted that in the
description below and in the drawings, the same elements are
identified with the same reference signs.
[0058] A device is used, for example, for determining the width
(CD--critical dimension) of a structure on a substrate 2. Also,
using the device, the position of a structure 3 on the substrate
can be determined. Although the device shown in FIG. 1 has long
been known from the prior art, for the sake of completeness, the
operation of the device and the arrangement of the individual
elements of the device will be discussed.
[0059] The device 1 comprises a measuring table 20, which is
arranged displaceable on air bearings 21 in a plane 25a, in the
X-coordinate direction and in the Y-coordinate direction. For the
mounting of the measuring table 20, bearings other than air
bearings can also be used. The plane 25a is formed from one element
25. In a preferred embodiment, the element 25 is granite. However,
to a person skilled in the art, it is obvious that the element 25
can be made from another material, which provides a precise plane
for the displacement of the measuring table 20. The position of the
measuring table is measured by means of at least one laser
interferometer 24 which, for the measurement, emits a light beam 23
which hits the measuring table 20. The element 25 itself is mounted
on oscillation dampers 26 in order to prevent building oscillations
reaching the device.
[0060] Placed on the measuring table 20 is a substrate 2, which
bears the structures to be measured 3. The substrate 2 can be
illuminated with a transmitted light illumination apparatus 6
and/or a reflected light illumination apparatus 14. The transmitted
light illumination apparatus 6 is provided in an optical
arrangement 40. The reflected light illumination apparatus 14 is
also provided in an optical arrangement 50. The optical arrangement
50 comprises the transmitted light illumination apparatus, a
deflecting minor and a condenser. By means of the deflecting
mirror, the light from the transmitted light illumination apparatus
6 is directed onto the condenser. The further optical arrangement
50 comprises the reflected light illumination apparatus 14, a
beam-splitting minor 12, the measuring objective 9 and a displacing
device 15 assigned to the measuring objective 9. Using the
displacing device 15, the measuring objective 9 can be displaced in
the Z-coordinate direction (e.g. for focusing). The measuring
objective 9 collects light coming from the substrate 2 and deflects
it out of the reflected light illumination axis 5 by means of the
partially transparent deflecting mirror 12. The light passes to a
camera 10 which is provided with a detector 11. The detector 11 is
linked to a computer system 16 which generates digital images from
the measurement values determined by the detector 11.
[0061] FIG. 2 shows an embodiment of the device 1 according to the
invention. An optical arrangement 50 is arranged above an optical
system support 100. The optical arrangement 50 comprises at least
one illumination apparatus 51. In addition to the optical system
support 100, a block 25 is provided. The block 25 and the optical
system support 100 are arranged such that they form an intermediate
space 110. Provided in the intermediate space is a first optical
element 9a (objective lens). This first optical element 9a is
arranged opposing a measuring table 20 which is arranged movable on
the block 25 in a plane 25a. The position of the measuring table 20
is measured with at least one interferometer 24 which directs a
laser beam 23 towards the measuring table. Provided on the
measuring table 20 is an object 2, in which the structures present
on the object 2 can be measured with the first optical element 9a.
The first optical element 9a is arranged in a reflected light
illumination apparatus in relation to the object 2. The light from
the illumination apparatus 51 passes via a deflecting mirror 60 to
the first optical element 9a. In the embodiment shown in FIG. 2,
the light beam from the illumination apparatus runs parallel to,
and over, the optical system support 100. It is also conceivable,
however, that the light beam from the illumination apparatus runs
parallel to, and under, the optical system support 100. In the
embodiment shown in FIG. 2, the optical system support 100 is
provided with a recess 102 in order that the light from the
illumination apparatus 51 can pass unhindered to the first optical
element 9a. A camera 10 is provided for recording the images formed
by the first optical element 9a of the structures 3 on the object
2. Furthermore, between the illumination apparatus 51 and the
deflecting minor 60, the optical arrangement 50 also has a beam
attenuator 52, a shutter 53, an apparatus for speckle reduction 54
and/or a homogenizer 55. In a particularly preferred embodiment,
the illumination apparatus 51 is configured as an excimer laser.
The illumination apparatus 51 has, for this purpose, a first outlet
57 via which the light generated by the illumination apparatus 51
passes to the first illumination branch 200. Apart from the
embodiment of the illumination apparatus 51 in the form of an
excimer laser, further promising alternatives for the design of the
illumination apparatus 51 are conceivable. One possibility for the
design of the illumination apparatus are so-called excimer lamps
which emit light in the same wavelengths as excimer lasers.
Furthermore, frequency-multiplied solid-phase lasers and gas lasers
can be used. Where, in the following, illumination apparatus and
light sources are mentioned, the three possible types of light
source that can be used in the present invention with an
expectation of success are always meant.
[0062] FIG. 3 shows another embodiment of the optical elements,
which are arranged in the first optical arrangement 50 over the
optical system support 100. The construction of the device 1 shown
in FIG. 3 is identical to the construction of the device as per
FIG. 2, except for the beam monitor 56. The illumination apparatus
51 has a first outlet 58 and a second outlet 59. Assigned to the
second outlet 59 is a beam monitor 56 with which the quality of the
light emitted by the illumination apparatus 51 can be monitored. It
is thus possible with the beam monitor 56 to determine intensity
variations of the illumination apparatus and to initiate a
corresponding correction so that a constant intensity always falls
on the substrate 2.
[0063] FIG. 4 shows an embodiment of the device 1 which is also
essentially identical to the configuration of the device according
to FIG. 3. In the following, not all the reference signs relating
to the elements shown in the drawings will be included so as to
ensure the clarity of the drawings and the associated description.
In FIG. 4, the illumination device 51 together with the beam
attenuator 52 and the beam monitor 56 are mounted laterally on the
device 1. In the case illustrated here, the illumination apparatus
51 is provided laterally on the block 25. The arrangement of the
device laterally on the block 25 is only one of several possible
embodiments of the invention. The light emitted from the
illumination apparatus 51 passes via the beam attenuator 52 to a
second deflecting minor 61. The deflecting mirror 61 is arranged
such that it directs the light into the first illumination branch
200 of the first optical arrangement 50. The light is thereby
deflected round the optical system support 100 and only then
passes, by way of the first deflecting minor 60, through the
optical system support 100 to the first optical element 9a. Due to
the heat generated by the illumination apparatus 51, it is useful
to arrange it as far as possible from the substrate 2 to be
measured. A particularly favourable arrangement is shown in FIG. 4.
An air stream 70 can be directed towards the illumination apparatus
51 which is arranged laterally on the block 25, by which means the
dissipation heat from the illumination apparatus 51 can be removed
particularly effectively.
[0064] FIG. 5 shows a further possible arrangement of the
illumination apparatus 41 in the device 1 according to the
invention. The illumination apparatus 41 is provided in the second
optical arrangement 40. The optical arrangement 40 is provided
beneath the block 25 of the device 1. The light emitted from the
illumination apparatus 41 reaches a deflecting mirror 62 and is
thereby deflected to a second optical element 9b (which functions
here as an objective lens), which partially reaches into the space
110 between the block 25 and the optical system support 100. The
second optical element 9a is arranged such that it is provided
opposite a substrate 2 which is laid on a measuring table 25.
Furthermore, the second optical arrangement 40 can comprise a beam
attenuator 42, a shutter 43, an apparatus for speckle reduction 44
and/or a homogenizer 45. The deflecting minor 62 can also be
constructed half-silvered so that the light coming from the
substrate and captured by the second optical element 9a passes to a
camera 10.
[0065] Depending on the orientation of the substrate on the
measuring table 20, the embodiment of the invention shown in FIG. 1
or FIG. 5 can be used both in the transmitted light arrangement and
in the reflected light arrangement. The orientation of the
substrate is intended to denote whether the structures 3 present on
the substrate 2 face in the direction of the first or the second
optical element 9a or 9b used for the investigation, or whether the
structures 3 present on the substrate face away from the first or
second optical element 9a or 9b used for the investigation. FIG. 9a
shows the substrate 2 in the conventional orientation which means
that the structures 3 on the surface of the substrate 2 face in the
direction of the first or second optical element 9a or 9b used for
the investigation. If the substrate 2 is inserted in the measuring
table 20 with this orientation, then the arrangement in FIG. 1 is
said to be a reflected light illumination arrangement. FIG. 9b
shows the orientation of the substrate 2 in the measuring table 20
wherein the structures 3 on the substrate 2 face away from the
first optical element 9a (in FIG. 1) used for the investigation. In
contrast thereto, however, the structures 3 on the substrate 2 face
toward the second optical element 9b in FIG. 5. If the substrate 2
is inserted in the measuring table 20 with the orientation shown in
FIG. 9b, the proposed arrangement of the first optical element 9a
as shown in FIG. 1 is said to be a transmitted light illumination
arrangement. With the arrangement of the second optical element 9b
as per FIG. 5, on the other hand, with the orientation of the
substrate as proposed in FIG. 9b, it is said to be a reflected
light illumination arrangement. In addition, the arrangement of the
substrate 2 shown in FIGS. 9a and 9b show that the substrate 2
experiences bending due to the support points on the measuring
table 20. The bending of the substrate 2 is represented in FIGS. 9a
and 9b by solid lines and the bend substrate is identified with the
reference sign 2d. The device as proposed in FIG. 5 is particularly
advantageous if the substrate with the orientation proposed in FIG.
9b is inserted into the measuring table 20 with the arrangement
proposed in FIG. 5. The arrangement proposed in FIG. 5 is thus used
in the reflected light arrangement. Therefore, with the arrangement
proposed in FIG. 5, the substrates can be measured with the same
orientation as they have in a stepper. Added to this is the fact
that with the apparatus as proposed in FIG. 5, the substrates are
measured with the same wavelength as used in a stepper if the masks
are illuminated on the wafer through the stepper.
[0066] FIG. 6 shows a further embodiment of the device as per FIG.
5, with the difference that the illumination apparatus 41 also has
a beam monitor 46 assigned to it. The beam monitor 46 is assigned
to the second outlet 49 of the illumination apparatus 41. Thus the
luminous power output by the illumination apparatus 41 can be
monitored by the beam monitor 46. Depending on the measuring result
from the beam monitor 46, the illumination apparatus 41 can be
adjusted accordingly so that the same intensity always falls on the
object 2.
[0067] FIG. 7 shows a further embodiment of the device, in which at
least the illumination apparatus 41 of the second optical
arrangement 40 is arranged laterally on the block 25. The light
from the illumination apparatus 41 is guided with a deflecting
minor 63 under the block 25 in the second illumination branch 300.
Otherwise, essentially all the components of the optical
arrangement 40 are identical to those in FIGS. 5 and 6 and do not
need further description here. In addition to the illumination
apparatus 41, the beam attenuator 42 and the beam monitor 46 can be
provided laterally on the block 25. The illumination apparatus 41,
which is configured as a laser or as a conventional excimer lamp,
causes heat generation. Through the arrangement of the illumination
apparatus 41 laterally on the block 25, it is possible for an air
stream 70 to be directed toward it to remove the dissipation heat
of the illumination apparatus 41. It is obvious to a person skilled
in the art that the air stream 70 should be guided in suitable
manner so that the dissipation heat is removed optimally.
Turbulence caused by the air stream must also be screened off so
that no other optical components of the device are influenced, as
this would falsify the measurement values obtained in a
non-reproducible manner. Mounting the illumination apparatus 41 on
the block 25 can be undertaken with suitable materials 80. Suitable
materials 80 have the property that they possess low thermal
conductivity. In order further to improve the removal of
dissipation heat, the material 80 may additionally be provided with
cooling ribs (not shown). These cooling ribs naturally lie in the
air stream 70 then.
[0068] FIG. 8 shows a further embodiment of the device, wherein in
the first illumination branch 200 and in the second illumination
branch 300, respectively, an illumination device 51 and 41 is
provided. Thus a separate illumination apparatus 41 is provided for
the reflected light illumination arrangement of the first optical
element 9a (here the objective lens). Similarly, for the
transmitted light illumination with the second optical element 9b
(here the condenser) a separate illumination apparatus 51 is
provided. In the first illumination branch 200, a shutter 53 is
provided. A shutter 43 is also provided in the second illumination
branch 300. The first shutter 53 and the second shutter 43 are
needed in the respective illumination branch 200, 300 in order to
switch between transmitted light and reflected light illumination.
If reflected light illumination is used or needed, the shutter 43
in the second illumination branch 300 is closed and vice versa.
Whilst the measuring table 20 is moving and no images are being
recorded, both shutters 53 and 43 are closed to reduce or avoid
exposure of the mask or the object 2 to the beam. For this purpose
the shutter 53, 43 can be arranged at any position in the first
illumination branch 200 or in the second illumination branch 300.
The arrangement of the shutter 43, 53 directly at the first outlet
48 or 58 of the first illumination apparatus 51 or the second
illumination apparatus 41 has proved particularly favourable. This
arrangement of the shutters 53, 43 also reduces the illumination
exposure of the various optical components in the first
illumination branch 200 and/or in the second illumination branch
300, and this also increases their service life.
[0069] FIG. 10 shows an embodiment of the invention, in which the
illumination apparatus 51 is mounted above the optical system
support 100. The device is configured such that with the device
both the reflected light illumination and the transmitted light
illumination can be performed as desired. A divider 65 is arranged
in the first illumination branch 200. The divider 65 directs part
of the light emerging from the illumination apparatus 51 through
the optical system support 100 and through the block 25 to a
deflecting mirror 63, which directs the illumination light into the
second illumination branch 300. In order to guide the illumination
light through for the second illumination branch 200 appropriate
recesses 106 and perforations 108 are provided in the optical
system support 100 and the block 25. As previously mentioned
several times in the description, the light from the second
illumination branch 300 is directed toward the second optical
element 9b (condenser). The light in the first illumination branch
200 is directed toward the first optical element 9a (objective
lens).
[0070] The embodiment shown in FIG. 11 differs from that in FIG. 10
in that the illumination apparatus 41 is arranged under the block
25. The light emitted from the illumination apparatus 41 into the
second illumination branch 300 initially meets a divider 66. From
the divider 66, part of the illumination light passes into the
second illumination branch 200. The other part of the illumination
light is deflected by the divider 66 and passes through the
perforations 108 and 106 in the block 25 and the optical system
support 100 to a deflecting minor 64 in the first illumination
branch 200. The light can thus be directed to the first optical
element 9a or the second optical element 9b as desired. As
mentioned above, in the first illumination branch 200, a shutter 53
is provided. Also in the second illumination branch 300, a shutter
43 is provided. Depending on the choice of whether transmitted
light illumination or reflected light illumination is desired, the
shutters 43 or 53 can be actuated accordingly so that light is
available in the first illumination branch 200 or in the second
illumination branch 300.
[0071] As shown in FIGS. 10 and 11, arranged downstream of the
first illumination apparatus 51 is a beam attenuator 52 Likewise,
arranged downstream of the second illumination apparatus 41 is a
beam attenuator 42. The beam attenuator 42, 52 serves to adapt the
intensity to the reflection of the light source in order to avoid
overdriving the camera 10 in the imaging channel. In principle, the
beam attenuator 52 or 42 can be arranged anywhere in the
illumination ray path 200 or 300. A sole condition for the
arrangement of the beam attenuator 52 or 42 is that in the first
illumination branch 200 or in the second illumination branch 300,
the beam geometry must be suitable for the beam attenuator 52 or 42
to be positioned at this site. In most beam attenuators, the
attenuation depends on the angle of incidence. Consequently, the
beam attenuator 52 or 42 is arranged at sites of small beam
divergence. Particularly advantageous is an arrangement of the beam
attenuator 52 or 42 directly behind the shutter 53 or 43. This is
advantageous since the optical components present in the rest of
the first illumination branch 200 or second illumination branch 300
are exposed to a lower beam intensity.
[0072] FIG. 12 shows an embodiment, in which the illumination
apparatus 41 is arranged laterally on the block 25. This
arrangement of the illumination apparatus 41 is essentially
identical to the arrangement of the illumination apparatus 41 in
FIG. 7. The light emerging from the illumination apparatus 41 is
again fed into the first illumination branch 200 and the second
illumination branch 300. For this purpose, again a divider 66 is
provided which directs the light beam emerging from the
illumination apparatus 41 through the recess 106 in the optical
system support and the perforation 108 in the block 25 to a
deflecting minor 64, which then feeds the light into the first
illumination path 200.
[0073] FIG. 13 also shows the illumination apparatus 41 arranged
laterally on the block 25. The difference from the arrangement
shown in FIG. 12 is that the illumination apparatus 41 has a first
outlet 48 and a second outlet 49. Arranged downstream of the first
outlet 48 of the illumination apparatus 41 is a beam attenuator 42.
Arranged downstream of the second outlet 49 of the illumination
apparatus 41 is a beam attenuator 52. The light from the
illumination apparatus 41 coming from the first outlet 48 and the
second outlet 49 is guided via a deflecting minor 63 or 64 into the
first illumination branch 200 or into the second illumination
branch 300. Provided in both the first illumination branch 200 and
the second illumination branch 300 is a shutter 43 or 53. With the
aid of the shutter 53, 43, the illumination can be controlled such
that, according to wish, reflected light or transmitted light
illumination is provided.
[0074] FIG. 14 shows an embodiment of the invention, in which the
illumination apparatus 41 is also arranged laterally on the block
25. Arranged downstream of the first outlet of the illumination
apparatus 41 is a shutter 43. Furthermore, a beam attenuator 42 is
arranged downstream of the shutter 43. Also arranged downstream of
the second outlet 49 of the illumination apparatus 41 is a shutter
53. Arranged downstream of the shutter 53 is also a beam attenuator
52. The illumination light for the first illumination branch 200
and the illumination light for the second illumination branch 300
is fed laterally past the optical system support 100 and laterally
past the block 25 in this embodiment. The light from the
illumination apparatus 41 is deflected by means of a deflecting
minor 63 into the second illumination branch 300. The light from
the illumination apparatus 41 which emerges from the second outlet
49 is deflected by means of a divider 66 into the first
illumination branch 200. Part of the light passes from the divider
66 to a beam monitor 56 with which, as mentioned several times
above, the intensity of the illumination apparatus 41 can be
monitored.
[0075] FIG. 15 shows an embodiment of the illumination apparatus
51. Although in the description below in relation to FIGS. 15 and
16, only the reference sign 51 is used for the illumination
apparatus, it is obvious to a person skilled in the art that the
same design conditions apply also for the illumination apparatus
with the reference sign 41. In FIG. 15, arranged downstream of the
illumination apparatus 51 is a shutter 53. In the embodiment shown
here, the shutter 53 is arranged directly downstream of the first
outlet 58 of the illumination apparatus 51. In the following
description, the illumination apparatus 51 is a laser. A beam
attenuator 52 is arranged downstream of the shutter 53. The beam
attenuator 52 has a first inclined plate 52a and a second inclined
plate 52b. The second inclined plate 52b has the same quantitative,
although opposite, angular position as the first inclined plate 52a
of the beam attenuator 52. The inclined plates 52a and 52b can be
provided, for example, with absorption filters in the known
embodiments. A particularly advantageous embodiment is when the
inclination angles of the individual plates 52a and 52b can be
adjusted. Depending on the chosen angular position, a predetermined
percentage of the light can be reflected out of the beam path. As
already mentioned above, the beam offset caused by the angled
position of a plate can be compensated for by a second angled plate
52b. If the angular position of the plates 52a and 52b is driven by
motor, the intensity level of the device can be set fully
automatically.
[0076] FIG. 16 illustrates the same device as in FIG. 15 except
that a beam monitor 56 is assigned to the second outlet 59 of the
illumination apparatus 51. The portion of the light 91 reflected
out by the first inclined plate 52a passes to a beam trap 92 and is
absorbed there. This also generates dissipation heat which must not
come near to the substrate or the mask. It is therefore
advantageous if the beam attenuator 52 is arranged geometrically as
far as possible from the mask and the substrate. As mentioned
several times in the description of the device, the illumination
apparatus 51 or 41 is arranged in an air stream so that the
dissipation heat can be carried away. Since the beam attenuator 52
is also situated immediately following the first outlet 58 or the
second outlet 59 of the illumination apparatus 51, the beam
attenuator is thus also arranged in the air stream, so that here
too, sufficient cooling and the removal of dissipation heat can be
carried out.
[0077] FIG. 17 shows an embodiment of the device wherein the device
1 is arranged in a housing which is configured as a climate chamber
500. The climate chamber 500 is connected to a control system 501
so that the desired pressure, humidity and protective gas
environment can be set and monitored. It might also be useful to
conduct the light reflected out of the beam attenuator (see FIG.
16) out of the climate chamber. The beam trap 91 can then be
arranged outside the climate chamber. The dissipation heat
therefore no longer comes close to the substrate or the object 2.
It is also useful to arrange the illumination apparatus 41 outside
the climate chamber 500. The climate chamber 500 has suitable
windows 510 which are transparent for the wavelength of the light
from the illumination apparatus 41, so that the light from the
illumination apparatus 41 passes into the interior of the climate
chamber 500. In the embodiment shown here, the illumination
apparatus 41 has a first outlet and a second outlet. A shutter 53
and a beam attenuator 52 can be arranged at each of the two
outlets. Part of the light from the illumination apparatus 41
passes from the divider 66 to a beam monitor 56, by means of which,
as mentioned several times above, the intensity of the illumination
apparatus 41 can be monitored. From the divider 66, the light from
the illumination apparatus 41 also passes into the first
illumination branch 200. The light from the illumination apparatus
41 can be deflected by means of a deflecting minor 63 into the
second illumination branch 300. It is obvious to a person skilled
in the art that the illustration shown in FIG. 17 is not a
limitation of the invention. What is important here is only that as
many of the components of the device as possible which produce
dissipation heat should be arranged outside the housing. An air
stream 70 for carrying away the dissipation heat from the
illumination apparatus 41 and other components which produce
dissipation heat is directed towards these. It is obvious to a
person skilled in the art that the air stream 70 should be guided
in suitable manner so that it produces optimum removal of the
dissipation heat.
[0078] FIG. 18 shows an embodiment of the device, in which the
overall ray path of the light from the illumination apparatus
inside and outside the climate chamber 500 is additionally provided
with an encapsulation 50a. The encapsulation 50a may be filled with
a suitable protective gas from a reservoir 400. Nitrogen has proved
to be a particularly preferable protective gas. The use of
protective gas is advantageous if for the illumination of the
object 2 a wavelength is chosen that is smaller than 220 nm. At
this wavelength, the level of absorption in the normal ambient air
is too high. The cause of this is mainly atmospheric moisture. In
order to keep losses small, flushing out with protective gas is
therefore necessary. Many dry, inert gases are suitable as
protective gases. As previously mentioned, the use of nitrogen is
particularly advantageous since it is inexpensive and safe to use.
In addition, hydrocarbons are always present in the normal ambient
air. Light of these short wavelengths breaks the hydrocarbons down
and the resulting decomposition products become deposited as a film
on the individual optical elements of the first optical branch and
of the second optical branch. As a result of the deposition of the
decomposition products on the optical components, the transmission
properties of these optical components become degraded. By means of
the protective gas flushing, therefore, this contamination by
hydrocarbons on the surfaces is avoided and the service life of the
optical components is extended. In the embodiment shown here, the
illumination apparatus 41, a shutter 43 and a beam attenuator 42
are provided outside the climate chamber 500. The shutter 43 is
useful since with it the light from the illumination apparatus 41
can be kept away from the remainder of the device when no
measurement is being carried out with the device. All the optical
components of the device are thereby protected from unnecessary
exposure to the beam, thereby extending their service life. The
light from the illumination apparatus 41 passes via a window 510
into the portion of the encapsulation 50a, which is situated in the
interior of the climate chamber 500. Part of the light from the
illumination apparatus 41 is guided via a divider 66 parallel to
the optical system support 100. Although in the representation
shown here, the light from the illumination apparatus 41 is guided
above the optical system support 100, this should not be regarded
as a limitation of the invention. From the divider 66, part of the
light passes to a deflecting minor which deflects the light such
that it is guided parallel to, and under, the block 25. Provided in
the light beam which passes parallel to the optical system support
100 and parallel to, and under, the block 25, in each case, are a
shutter 53, an apparatus for speckle reduction 54 and a homogenizer
55.
[0079] As described above, the optical arrangement 40 or 50 can
also comprise a homogenizer 55 or 45. The homogenizer 55 or 45
serves to illuminate the object field and the pupil evenly. The
even object illumination ensures that the measuring result does not
depend on the location of the structure 3 being measured within the
object field. Uneven pupil illumination leads to systematic
measuring errors, which depend on the actual size of the structure
3. To avoid this, in critical applications, as in the measurement
of the positions of structures 3 on an object 2, the pupil is
homogenized.
[0080] If a laser is used as the illumination apparatus 51 or 41,
the level of coherence of this light source is too high and
speckles occur. This leads to a flecked and very noisy image and is
not suitable to be used for the measurement of positions of
structures 3 on an object 2. During evaluation, speckles of this
type lead to errors in the positional determination. In order to
avoid this, it is necessary to use an apparatus for speckle
reduction 54 or 44. These apparatuses are essentially based thereon
that averaging is carried out over a plurality of images, thereby
ensuring that the speckles are not constant over time. This can be
done by one of the following methods.
[0081] If a pulsed light source is used, then the speckle pattern
changes between two pulses. It is possible therefore to average
over a plurality of individual images. With continuous light
sources, rotating ground glass disks suggest themselves. The
averaging then takes place within the exposure time. It is also
conceivable to use a glass fibre with mode mixing properties.
Averaging can then be achieved using these glass fibres.
[0082] The illumination apparatus 51 or 41 (except the excimer
lamp) are pulsed light sources. With these, inevitably variations
in the intensity occur from pulse to pulse. In order to detect
large anomalies or to be able to correct the actual pulse energy,
it must be recorded together with the measurements. Advantageous
for this is the arrangement of a beam monitor 56 directly behind
the beam attenuator 52. The measuring result from the beam monitor
56 can thus be used for automatic setting of the beam attenuator
52.
[0083] Also advantageous is the detection of the intensity before
the first optical element 9a (objective lens in the reflected light
case) or before the second optical element 9b (condenser in the
transmitted light case), since at this point, losses in the optical
path to this point are detected. With progressive degradation of
the optical components, the results from intensity measurements
made directly in the vicinity of the illumination apparatus 41 or
directly after the beam attenuator 42 no longer match the intensity
that finally reaches the object 2 or the mask. This would also lead
to false results in the measurement of the position of the
structure. The use of the measured intensity to correct the results
when measuring the position of structures 3 on an object 2 and for
determining the degradation of the optical system is therefore
advantageous.
[0084] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *